This invention relates generally to steering column assemblies for automotive vehicles, and more particularly to such assemblies fitted with energy absorbing devices which are operative to absorb kinetic energy in response to collapse of a steering column in the event of a crash.
Steering column assemblies for automotive vehicles are known to be equipped with various energy absorbing (“EA”) devices which serve to absorb kinetic energy of a collapsing column in the event of a crash. In a sudden frontal impact situation, there are conditions under which the driver may be thrown forward against the steering column, particularly if the driver is unbelted. Many steering columns are designed to collapse under such conditions. EA devices are designed to cooperate with collapse of the column in order to absorb a certain amount of the kinetic energy of the collapse in an effort to alleviate the full force of impact to the driver.
Depending upon various factors, the requirements of the EA device may differ. For example, a situation in which a very heavy driver is seated far away from the steering wheel and is unbelted would call for greater energy absorption on the part of the EA device than would that required in a situation involving a very light occupant seated closer to the steering wheel. Various parameters have been taken into account in the design and manufacture of so-called adaptive EA systems, which measure one or more parameters and then make adjustments in the EA system prior to impact to increase, decrease or in some way alter the behavior of the EA system in the event of a crash. For example, in the heavy, unbelted driver situation above, the EA system could react by adjusting the number, position or size of an anvil(s) across which one or more EA straps are drawn in order to increase the amount of energy absorbed in a crash to accommodate the relatively greater forces from such a driver, as compared to a lighter driver where the reverse may be done. This ability to adapt to various parameters can help manage the absorption and dissipation of the energy of the collapsing column when impacted by the driver. Such adaptable EA systems are able to adjust their energy absorption characteristics by altering the position or configuration of the energy absorbing components. For example, an EA device may be fitted with an S-strap routed about two anvils in a pre-set condition to provide a high level of energy absorption, but may be adjusted by sliding one of the anvils out of the way of the path of the S-strap in order to provide a relatively lower energy absorption condition. Other arrangements employ multiple straps, wires, and other arrangements which can be altered in arrangement, quantity, or configuration in order to adjust the energy absorbing characteristics. The known adaptive EA systems are constructed such that the movable anvil or other components which get altered when the device adapts to a changing condition are all contained within a closed housing of the EA system and thus it is not readily apparent upon external inspection of the EA device which of two or more positions of adjustment it may be in. For example, the EA device in which an S-shaped EA strap is initially wrapped about two anvils but adjustable to eliminate one of the anvils and thereby reduce the energy absorbing characteristics of the EA system does not provide a means of telling which position the movable anvil is in at the time the device is installed in the vehicle and during the service life of the vehicle. In the event the device is inadvertently moved to the second position, such as if the vehicle is involved in a collision sufficient to activate the adaptive system, and the operator continues to use the vehicle without repairing or replacing the EA device, the full performance of the device may be diminished.
It is an object of the present invention to provide a means of telling which position an adaptable EA device is in at any given time during its service life.